The Dark is Rising sequence, by Susan Cooper is a mix of Arthurian legends and Irish/Scottish/Welsh folktales where good battles evil in an epic battle that spans all time. Will Stanton is the youngest of the Old Ones, and he is vitally important to this fight. The three Drew children, Simon, Jane, and Barney, are also connected to the fight between the Light and the Dark in ways that even they don't understand.
In Over Sea, Under Stone, the three Drew children are staying in the seaside village of Tressiwick with their Great-Uncle Merry, who, although he isn't actually related to them, has been a part of their family for as long as they can remember. When Barney finds an ancient map in the attic of the cottage they're vacationing in, it sets them off on a dangerous quest to recover something that will help the Light defeat the Dark forever: the grail. But agents of the Dark have learned about the map as well and they are closing in. I liked the atmosphere of this one - when I started I expected some fluffy story about three kids having a wonderful vacation on the seaside. What I got was just the tip of the iceberg of a very epic, fantastic story that just got bigger and better the further into the series I went.
Book three of this series, The Greenwitch, is where Will and the Drew children meet for the first time. There's some tension at first as the four of them figure out how to work together, but they've got a very important job to do. The grail has been stolen by the Dark and they have to get it back. Also, a being that belongs to neither the Light or the Dark has possession of a clue that will help strengthen the Light. The Greenwitch is a creature of wild Magic, reborn every year by the women of Tressiwick in a ritualistic ceremony. Together will Merriman Lyon, also known as Great-Uncle Merry, Will and the Drew's have to retrieve the grail and strike a bargain with the unpredictable Greenwitch. What I liked about this book was that this time around, the Old Ones didn't hold all the answers, and the Drews played a very important part in the story, even though they were basically ordinary human beings.
The Dark is Rising sequence was a thoroughly interesting read. It was a pretty epic adventure, but didn't meander on for hundreds and hundreds of pages. It was to the point, which I appreciated because I could really get at the good parts of the story without having to read 2000 pages to get there. I also really liked Will, Bran, and the Drew's. Sometimes Merriman saved the day once too often, but he is the first of the Old Ones, so he has been around for basically forever and it would take a lot to defeat him. Also, the prominence of Arthurian legends and old folktales in the background of these stories was really intriguing. I've always loved mythology of any kind, and Scottish and Irish mythology isn't involved in stories as often as Greek mythology is, so it was a treat to find it here. And lets not even get started on Welsh folklore! After reading these books, I'd really like to see Wales and read some old Welsh stories.
In other words, thank you, Katie! If you hadn't suggested this series I might never have picked it up on my own!
Link to author website: http://www.thelostland.com/works/yabooks/bk_dircollector.html